The present invention relates to pulsed radar apparatus and methods, and, more particularly, to power distribution systems employed in such apparatus.
In state-of-the-art, ground-based or airborne pulsed radar apparatus, active electronically scanned arrays (AESAs) generate radar beams which have a digitally controlled magnitude and direction. AESAs are fixed in position and thus generate radar beams without need for array motion when a change is to be made in beam direction.
AESAs have numerous, small-beam generating units (such as gallium arsenide RF amplifiers) which are individually controlled in phase and magnitude to produce a collective radar beam having a specified direction and magnitude. A modulating power distribution system applies modulating power pulses to the individual units to provide the radar beam energy and to pulsate the collective radar beam at a specified radio frequency.
The system generates the modulating pulses up to a radio frequency, with each modulating pulse having a fast rise time and a fast fall time. Flat top portions of successive pulses are required to contain no more than an extremely small ripple.
A DC generator normally operates as a voltage source for the power distribution system and a digital system provides logic and other system functions in the radar apparatus. Conventionally, a dissipative DC-DC low voltage converter is used to reduce the source voltage, such as 270 volts, to a lower DC voltage, such as 10 volts, which is applied to a dissipative, linear regulator/modulator. In turn, the regulator/modulator generates the modulating power pulses which are output to one or more associated AESA RF amplifier units. The digital system generates logic signals to control the modulating frequency of the modulating power pulses generated by the converter and applied to the AESA.
Capacitor and filter elements are disposed in the power distribution system to provide energy storage which reduces peak demand on the voltage source.
A bus system is employed to interconnect the described power distribution system components. Numerous bus connections are required at a lower level of the power distribution system because of the large number of AESA RF amplifiers.
At higher system levels, buses can be quite large and weighty because of the current amplitudes needed to supply a large number of AESA RF amplifiers. In airborne radar apparatus, bus weight can be significant even where the low voltage DC source is within 2 or 3 meters of the AESA circuitry. Bus system weight can be controlled through architectural and mechanical design, but only to an extent limited by the overall design of the power distribution system.
In addition to being undesirably heavy, conventional power distribution systems operate with undesirably low efficiency. Typically, a power distribution system, of the type considered above, operates with an efficiency of 65% or less. In another known power distribution system design called a distributed power supply configuration, many small, low voltage power supplies are distributed over the AESA to save bus weight, but overall power distribution system efficiency is restricted by the use of linear regulator/modulators and is thus little better at about 67%.
Some effort has been made in the prior art to improve the efficiency, weight, and other characteristics of distributed power supply systems. For example, U.S. Pat. No. 5,410,276, entitled RF MODULATION USING A PULSED DC POWER SUPPLY and issued to William B. Hwang et al. on Apr. 25, 1995, discloses a system in which a very high frequency (VHF) converter is employed in the generation of modulating power pulses for an AESA.
However, the Hwang patent restrictively applies a VHF converter in an AESA power distribution system only to eliminate the conventional use of a linear regulator/modulator, enable direct modulation of the high power RF amplifier circuitry, and, as restrictively applied, enable only improvements in the AESA operating circuitry coupled between the VHF converter and the AESA. For example, Hwang cites reduced downstream energy storage capacitance located on the AESA, reduced size through elimination of conventional modulation circuitry for the RF amplifiers, etc. In an earlier U.S. Pat. No. 4,980,810, entitled VHF DC-DC POWER SUPPLY OPERATING AT FREQUENCIES GREATER THAN 50 MHZ and issued to R. F. McClanahan et al. on Dec. 20, 1990, the disclosure is limited to VHF converter circuitry.
A need thus exists to improve pulsed radar apparatus such that power distribution is provided for AESA radar pulse modulation with significantly greater efficiency and reduced weight for the power distribution system as a whole as opposed to just a portion of it. It is further desirable that such power distribution be provided with greater whole system reliability and lower, whole system cost.